Syrian rebels fighting President Bashar al-Assad’s regime are now armed with man-portable air defense systems (MANPADS) including US-made Stingers, Russia’s top military commander said on Wednesday.

Russia has “reliable evidence” that the rebels have the weapons, “including US-made Stingers,” but “who delivered them, we need to look into,” Army Headquarters General Nikolai Makarov said.

NBC news reported in August the rebels had been supplied with unspecified MANPADS, possibly initiated by Turkey, Saudi Arabia or Qatar which have repeatedly called for lending military support to the Syrian opposition.

US State Department spokeswoman Victoria Nuland said she could not confirm whether the rebels had been supplied with such missiles, and maintained the United States was against the uncontrolled spread of MANPADS.

“We have already made it clear how much we are concerned about the treatment of this type of weapons around the world. We work with governments trying to withdraw MANPADS from circulation,” she said on October 16.

Russia has previously stated it regards the rebels’ acquisition of MANPADS as a dangerous development.

“Arming the Syrian rebels with such a dangerous weapon as MANPADS, or sanctioning such actions, would be a most dangerous act,” Russian Foreign Ministry spokesman Alexander Lukashevich said earlier.

In 2003, over 95 countries signed the Elements of Export Controls for MANPADS, which was later updated. A further agreement on restricting proliferation of MANPADS was signed in May 2004 by the Organization of Security and Cooperation in Europe, including the United States.

While there has been no conclusive proof of use of MANPADS in Syria, various rebel groups have claimed they possess them, and videos posted on YouTube earlier this month appear to show rebels in Aleppo armed with Soviet-era SA-7 Strela missiles, the world’s most widely-produced MANPADS weapon.

“Opposition groups have now at least the Strela-2 (SA-7 Grail) – most likely acquired from Assad’s own forces, and it is possible that a smaller number of Stinger MANPADS are also now in their possession,” said Douglas Barrie, an air warfare analysts with the London-based International Institute for Strategic Studies. “The acquisition of man-portable surface to air missiles will improve their ability to provide rudimentary low-level air defense against combat aircraft and helicopters.”

Several videos have also been posted appearing to show Mi-8 helicopters and MiG-23 fighter-bombers being shot down by Syrian rebels, although the weapons used appear to be heavy machine guns rather than surface-to-air missiles.

The US-made General Dynamics Stinger was supplied in the hundreds to the Mujahideen forces in Afghanistan during the Soviet Union’s military campaign in the 1980s, and made a radical impact on the use of Soviet air power there, according to the then-head of Pakistan’s Inter-Services Intelligence Agency, Mohammed Yousaf, who was involved in supplying them.

The US Central Intelligence Agency later set up a “buy-back” operation in a bid to recover the weapons after the Soviet Union withdrew its forces from Afghanistan, amid concern that the weapons could be used by radical Islamist groups to shoot down a civilian airliner.

MANPADS are shoulder-launched missiles which can be carried and fired by one person. Usually guided by infra-red seekers that home in on an aircraft’s engine heat, they can often hit targets as high as 13,000 feet at a range of up to a few miles, and are especially dangerous to large and slow aircraft like civilian airliners and helicopters. Several civilian aircraft have been shot down with MANPADS since the late 1970s.